In the abrasive industry there is a trend to finer and finer surface finish. Naturally, to achieve these finer surface finishes, smaller sized abrasive particles are employed in the abrasive article. In some instances the particle size of these small sized abrasive particles is less than 50 μm, typically less than 25 μm and sometimes less than 10 μm. In some instances loose abrasive slurries are employed rather than using fixed abrasive articles where the abrasive particles may be bonded together (to provide a bonded abrasive product) or to a backing (to provide a coated abrasive product). Many years ago, these loose abrasive slurries were capable of achieving surface finishes that were not previously obtainable with fixed abrasives. Over the last years, however, advances in fixed abrasives, especially coated abrasives, have enabled coated abrasives to effectively replace loose abrasive slurries in certain applications and thereby avoid the liquid handling equipment required for, and the waste disposal problems associated with, the use of slurries.
In many instances to achieve a fine surface finish, the polishing process is done in the presence of a fluid, typically water or some other type of lubricant. The fluid serves several purposes including minimizing heat build up and serving as a medium to remove the swarf or debris generated during polishing. If the swarf is not effectively removed during polishing, it is possible for the swarf to become re-deposited on the abrasive coating and thereby may cause coarse and undesirable scratches. Thus, it is imperative that the swarf be removed to provide efficient fluid flow at the interface between the abrasive coating and the workpiece surface being polished.
For all of the benefits of the fluid, there are sometimes drawbacks. For instance, with the very small abrasive particles, the resulting outer surface of the abrasive coating may be relatively smooth. The combination of the fluid and smooth abrasive coating has been known to create what is known in the industry as “stiction,” whereby the fluid will act like adhesive between the abrasive coating and the workpiece surface to cause these surfaces to stick together with unwanted results.
Stiction typically occurs in lapping type coated abrasive products. There are two common types of coated abrasive products. The first type has the abrasive particles bonded to the backing by means of a make coat. Overlying the abrasive grains is a size coat, which further reinforces the abrasive grains. In this first type, there is essentially one or two layers of abrasive particles. In the fine grades, the abrasive particles are so small that the resulting coated abrasive may exhibit a relatively short life. The second coated abrasive construction has the abrasive particles dispersed, typically uniformly dispersed, in the binder. This second construction is sometimes referred to as a “lapping film.” The lapping film may have longer life because there typically are multiple layers of abrasive particles as compared to the construction with the make and size coats. Likewise, the lapping film may produce a finer surface finish because the abrasive particles are more embedded in a binder. Conversely, lapping films tend to have lower cut rates since the first type construction tends to have more abrasive particles protruding.
Stiction tends to occur more frequently with lapping-type construction because the abrasive particles are embedded in the binder to provide a smooth surface. Various lapping type products have been provided with an abrasive coating which is shaped or structured, i.e., having raised portions and recessed portions. These products are sold by Minnesota Mining and Manufacturing (3M) Company under the trade designation “TRIZACT™” abrasive products. They are generally described in U.S. Pat. No. 5,152,917 (Pieper, et al.). Other lapping products are also described in U.S. Pat. No. 5,489,235 (Gagliardi, et al.).